It's a machine with a built in computer. I'm not familiar with babylocks, but with the Vikings, software updates, such as enhancements and fixes are loaded this way. Also, new decorative stitches are occasionally available. The updates are available online or you can bring a USB device to your dealer. They load the update then you take it home & put it on your machine. when the updates are available, instructions are also provided to install them.
The USB on the Crescendo was probably put there for the same reasons, but babylock may have not needed to update the software nor offered additional features or stitches. If your dealer doesn't know about any updates, don't worry about it! Here's a link to the last update info. You probably have a newer machine and didn't need it:
http://www.babylock.com/ftp/whitepap...fo_Website.pdf